1. Field of the Invention
The present invention relates to a controller for a tone signal synthesizer of an electrical musical instrument, and more particularly to a controller for a physical model tone signal synthesizer electronically simulating a sound generating mechanism of a natural musical instrument.
2. Description of the Related Art
As one of tone signal synthesizer circuits of electronic musical instruments, there is known a tone signal synthesizer called a physical model tone signal synthesizer of the type which simulates the sound generating mechanism of a natural musical instrument. Such a synthesizer is suitable particularly for stringed instruments and wind instruments which generate continuous sounds. For the generation of musical tones of stringed instruments, a pitch signal as well as a bow pressure, a bow speed signal, and the like are required. For the generation of musical tones of wind instruments, a pitch signal as well as a breath signal, embouchure signal, and the like are required.
Referring to FIG. 17, an example of the structure of a physical mode tone signal synthesizer will be described. The description is first directed to stringed instruments.
Bow speed and pressure information is supplied via gates 112 and 120 which are opened (turned ON) in response to a key-on signal and closed (turned OFF) in response to a key-off signal.
Bow speed information supplied while the gate 112 opens in response to the key-on signal, is inputted to an adder 113 and, via an adder 115 and subtracter 117, to a non-linear circuit 118. The non-linear circuit 118 simulates the non-linear characteristics of a stringed instrument. This circuit 118 outputs a signal proportional to an input signal when the latter is small, and outputs a signal smaller than, and non-linearly changing with, an input signal when the latter is larger than a predetermined value.
Such a characteristic provides an approximate alternative of a motion of a string of, for example, a violin determined by static and dynamic friction coefficients of the string and bow. An output of the non-linear circuit 118 is supplied via a multiplier 119 to adders 125 and 126.
The adders 125 and 126 are positioned symmetrically on a transmission line forming a closed loop. This closed loop provides an approximate alternative of a motion of a string of a stringed instrument, and includes a pair of delay circuits 128, 129, a pair of low-pass filters 131 and 132, a pair of attenuators 134 and 135, and a pair of multipliers 137 and 138.
The delay circuits 128 and 129 provide a delay of a signal circulating the closed loop, and determine a pitch of a tone to be generated. The pair of delay circuits 128 and 129 provide approximate alternatives of two string portions, one being a string portion from a fixed end or fret to the drawing position of a bow across the string, and the other being a string portion from the drawing position to the position of a finger pressing the finger board.
While a vibration transmits over the string, this vibration signal changes with the characteristics of the string. The vibration attenuates while transmitting over the string. The pair of attenuators 134 and 135 control the attenuation amounts to simulate the attenuation of a signal transmitting over the string. When a key-off signal is inputted, the attenuation amounts increase greatly to stop the vibration of the string.
The vibration of the string reflects from the fixed end or fret, and the phase is inverted at the fixed end. The multipliers 137 and 138 multiply their inputs by a fixed coefficient "1". In this case, the phase is inverted by the reflection without attenuation. In an actual case of a natural musical instrument, although the vibration is attenuated by such a reflection, this attenuation can be taken into account by adding it to the attenuators 134 and 135.
The delay circuits 128 and 129 and low-pass filters 131 and 132 are supplied with a tone color signal to adjust the signal waveform. As a signal circulates the closed loop, the motion of a vibration transmitting over the string and reflected to the initial position can be simulated.
The outputs of the multipliers 137 and 138 are supplied to an adder 140. This represents that the vibrations travelling from opposite sides are supplied to the drawing position. Both the inputs incoming from opposite sides are added together by the adder 140, and the result is supplied to the adder 113 to be added to the current bow speed signal.
Namely, while a continuous sound is generated by drawing the bow across the string, a vibration of the continuous sound generated by the string is added to the a vibration newly generated by drawing the bow across the string, to generate a resultant musical tone.
The non-linear circuit 118 has a divisor 117 on the input side and a multiplier 119 on the output side. The divisor 117 and multiplier 119 receive a bow pressure signal via the gate 120.
Specifically, an input to the non-linear circuit 118 is changed to a small signal through the division by the bow pressure signal, and an output from the non-linear circuit 118 is changed to a large signal through the multiplication by the bow pressure signal. In other words, if the characteristic of the non-linear circuit 118 is fixedly set, the input and output signal scales of the non-linear circuit 118 change with the bow pressure signal. This simulates that as the bow pressure signal becomes large, the linear portion of the characteristic is expanded to broaden the static friction coefficient area.
An output of the multiplier 119 is fed back to the adder 115 via a low-pass filter 122 and adder 123. The characteristic of the non-linear circuit 118 has a linear portion representing the static friction coefficient and a small output portion representing the dynamic friction coefficient on the outer side of the linear portion, both the portions being stepwise switched.
As an input signal to the non-linear circuit 118 becomes large to the extent that it enters the region governed by the dynamic friction coefficient, the output becomes small and the feedback amount fed back to the input side via the feedback loop reduces accordingly. If an input signal is reduced after it once entered the dynamic coefficient region, the feedback amount is small corresponding to the small output signal. Therefore, switching between both the portions occurs by a small signal value.
Near the switching region, the feedback amount when an input signal to the non-linear circuit 118 is increasing is different from that when an input signal is decreasing, providing the characteristic with a hysteresis.
The low-pass filter 122 is provided for preventing oscillation or the like. In the tone signal generating circuit shown in FIG. 17, the pitch information as well as the bow speed and pressure information are used as important parameters for generating tone signals.
In the case of wind instruments, in place of the bow speed and pressure signals, a breath signal "pr" and an embouchure signal "em" are used. The breath signal "pr" represents the pressure information of breath blown from a mouthpiece, and the embouchure signal "em" represents the embouchure of a player. The breath signal serves as a drive source of vibrations, and the embouchure signal is used for controlling the tone color or the like. The divisor 115, non-linear circuit 118, and multiplier 119 are replaced by a non-linear circuit representing vibrations within the tube of a wind instrument. The closed loop including the delay circuits 128 and 129 is replaced by a circuit representing the tube of a wind instrument in which vibrations reciprocate.
As methods of controlling such a physical model tone signal synthesizer, there is known a method which uses a velocity and after-touch obtained from keyboard manipulators. There is also known a method which used wind controllers and stringed instrument manipulators, obtains a breath signal, embouchure signal, bow speed signal, bow pressure signal, and the like from sensors provided to controllers and manipulators, and supplies them to a physical model tone signal synthesizer.
Single data supplied to a physical model tone signal synthesizer gives various influences to a generated tone. For example, consider a wind instrument, the sound volume is controlled mainly by a breath signal and the tone color is controlled mainly by an embouchure signal. However, if the breath signal is increased to increase the sound volume, the tone color is also changed, or conversely if the embouchure signal is changed to change the tone color, the sound volume is also changed.
In order to increase the sound volume without changing the tone color, it is necessary to increase the breath signal and decrease the embouchure signal. This corresponds to that in increasing the sound volume of, for example, a natural instrument saxophone, the embouchure first relaxes to ease the vibration of a reed, and then a breath is strongly brown.
Furthermore, even if an embouchure signal only is changed to change the tone color while maintaining the sound volume unchanged, the sound volume will change. It is therefore necessary in this case to change the embouchure signal and adjust the breath signal.
Also in the case of stringed instruments, the sound volume depends mainly on the bow speed signal, and the tone color depends mainly on the bow pressure signal. However, both the sound volume and tone color are not determined only by the bow speed or bow pressure. As above, the input parameters to the physical model tone signal synthesizer and target musical tone characteristics have no one-to-one correspondence, and they are related to each other in a complicated way.
An envelope generator EG for generating input parameters in a physical model tone signal synthesizer is an essential means for driving the synthesizer using a keyboard. A conventional envelope generator EG generates envelopes of control parameters of the synthesizer. If such an envelope generator is driven by a velocity or after-touch signal, it is almost impossible to independently control various musical characteristics.
Wind controllers and stringed instrument manipulators provided for giving a performance like that of natural musical instruments and directly control input parameters to the physical model tone signal synthesizer. Therefore, if performance know-how is learned through exercise, it is possible to produce desired musical tone characteristics.
However, such exercise requires to master algorithms and manipulators in order to produce desired musical tones using manipulators. It is practically impossible for a general keyboard player to give a desired performance.
As described so far, it is not easy for most players to give a performance satisfying desired musical effects by using a physical model tone signal synthesizer.